Why Do We Yawn?

My husband and I often play a Google game: We type in the beginning of a question, then let Google fill in the rest. It's always funny (and sometimes disturbing) to see what's most often on people's minds. So, I figured, why not do a service to society, and answer these most burning questions? (I know this isn't about decorating or baking. But this interests me, so there!) 


So, Why Do We Yawn?

Just looking at this kitty may make you yawn.

Until recently, the answer to this eternal question would have made you yawn: Scientists simply didn’t know why we open wide when we’re tired. Lucky for you—you curious Googler, you—a 2013 study review from India summed up all the newest research that points to potential purposes of yawning.

Theory #1: Yawning is like a shot of energizing caffeine to your body. According to the researchers, “evidence suggests that drowsiness is the most common stimulus of a yawn." No surprise there. But bedtime isn’t the only time drowsiness sets in—it may also be induced by boredom, which stimulates your sleep system.

So, when you brain is nodding off, yawning may be a way to spike your heart rate and boost your arousal, much in the same way that caffeine does. How? The physical motion of opening your mouth compresses your “carotid body”—a small cluster of sensory receptors in your carotid artery—and this may trigger the release of alerting hormones.

Theory #2: Yawning is a way to cool down your brain. In a recent study, researchers found that three minutes before rats yawned—yes, they yawn too!—their brain temperature was higher than normal. After they yawned, their brains dropped a few degrees. Another study showed that as room temperature rose, parakeets started yawning more frequently.

And, finally, research in humans revealed that when people placed a cold pack on their foreheads, they yawned less than when they held a warm pack to their head. (The scientists note that it may not be so much about brain temperature, though, as the arousing effect of feeling cold.)

So how might yawning act like a fan for your gray matter? Simple: The contraction and relaxation of muscles in your face boosts blood flow, which helps dissipate heat. And if your eyes water during a yawn—as many people’s do—more heat may be drawn from your skull.

Theory #3: We yawn to bond. You know that annoying (and embarrassing) urge to yawn because your neighbor did? Well, you can pat yourself on the back, because it may be a subconscious expression of empathy. Seeing someone else’s mouth gaping open may activate your brain’s mirror neurons, which tell your body to mimic the behavior you're watching—especially if that person is a family member or close friend.

Theory #4: Yawning shields your ears from damage. When you need to pop your ears, what do you do? You open your mouth. Likewise, yawning may serve as a “defense reflex”—a way to protect your ears in situations (like rapid altitude changes) that could trap air in your middle ear. However, because swallowing can also offer this same benefit, this probably isn’t the sole purpose of yawning, the scientists say.

Debunked Theory: Yawning is a sign you're oxygen deficient. For centuries, scientists and laypeople alike thought that yawning removed “bad air” from the lungs and increased oxygen traffic to the brain. However, studies have now shown that people don’t yawn any more than normal when they inhale high amounts of carbon dioxide—which should trigger a need for oxygen, and therefore yawning, if this theory were true.